Prosthetic joint system for bone replacement

ABSTRACT

A prosthetic joint system is provided for use when replacement of bone is required. The system includes an elongated stem having a joint motion surface at one end and an outside surface which includes at least one tapered portion, a sleeve for fixation to the patient&#39;s bone which has an internal taper for locking engagement with the at least one tapered portion, and a bone replacement element which can be a bone graft. The system includes means for attaching the bone replacement element to the stem at a location between the joint motion surface and the sleeve. In the case of bone grafts, the system can include a second sleeve for implantation in the graft and a second tapered portion on the stem for locking engagement with the second sleeve. Preferably, a series of mating stems, sleeves, and bone replacement elements, or second sleeves in the case of bone grafts, are provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to prosthetic joints and, in particular, to aprosthetic joint system for use when bone replacement is required.

2. Description of the Prior Art

Various prosthetic joints are known which include means for replacingbone which the patient has lost as a result of disease, trauma, orbio-mechanical degeneration caused by, for example, a previous jointimplant.

FIG. 1 shows a two piece prosthesis 14 of this type which includes astem 16 and a bone replacement portion 18 which can be a bone graft or ashaped part composed of a plastic material, such as ultra high molecularweight polyethylene (UHMWPE). See "Link Endo-Model Total FemurReplacement", Link America, Inc., East Hanover, N.J., 1989, and "TheLeinbach Horizontal Platform Femoral Component", Allo Pro Corporation,St. Petersburg, Fla., 1982.

FIG. 2 shows another prior art construction of this type which comprisesa one piece metal prosthesis 10 which includes a proximal portion 12which serves as a replacement for bone. Examples of prostheses of thisgeneral type include those sold by Howmedica under the productdesignations "Universal 32 mm Proximal Femur Total Hip Components withPolished Loops", "Muller Type 32 mm Proximal Femur", "Harris CalcarReplacement 32 mm Total Hip System", and "Averett Modified Head Neck 32mm Total Hip System", and those sold by DePuy under the productdesignation "1031-30/44 Femoral Upper Third".

Although these prostheses have benefited many patients, problems haveremained with their use. In particular, with reference to the prosthesesof the type shown in FIG. 2, custom prostheses are often needed and evenwhen customized, these prostheses may not fit the patient particularlywell, especially in connection with achieving a tight fit between theprosthesis and the patient's bone. These prostheses provide the surgeonwith only one choice of replacement at the time of surgery which limitsthe ability of the surgeon to respond to specific needs or problemsascertained after the surgery has begun. Also, custom prostheses take asubstantial amount of time to fabricate and are expensive.

With reference to the prostheses of the type shown in FIG. 1, these canprovide the surgeon with some degree of choice at the time of surgery.Typically, a family of stems and a corresponding family of replacementportions 18 are provided to the surgeon. Also, in some cases, parts ofthe replacement portion can be cut away at the time of surgery toaccommodate different amounts of bone loss. See the Allo Pro system,supra. However, these prostheses still suffer from problems in achievingan optimum interface between the stem 16 and the patient's bone. Inparticular, because of the mechanical configuration of the prosthesis,porous coating of the stem to achieve long term fixation through boneingrowth is inadvisable since it may reduce the endurance strength orthe stem.

Femoral prostheses which include sleeves for engagement with bone arealso known in the art. See, for example, Noiles U.S. Pat. No. 4,846,839and Noiles U.S. Pat. No. 4,790,852. Such prostheses have not includedseparate bone replacement elements of the type shown in FIG. 1 but insome cases have included an integral bone replacement portion of thetype shown in FIG. 2.

SUMMARY OF THE INVENTION

In view of the foregoing state of the art, it is an object of theinvention to provide improved joint replacement prostheses having bonereplacement means. In particular, it is an object of the invention toprovide a modular system whereby the surgeon can select the set ofcomponents most suitable to the patient's condition as determined at thetime of surgery.

It is a further object of the invention to provide prostheses of theforegoing type having an improved interface between the prosthesis andthe patient's bone. In particular, it is an object of the invention toprovide a prosthesis employing a sleeve for engagement with the bone anda stem which interlocks with the sleeve. In this way, the sleeve can beoptimized for size, shape, and surface characteristics vis-a-vis boneengagement without structurally comprising the overall strength of theprosthesis.

It is an additional object of the invention to provide improved meansfor attaching a bone graft or other bone replacing material to a bonereplacement prosthesis which again allows selection of the optimumcomponents at the time of surgery.

To achieve the foregoing and other objects, the invention provides aprosthesis for implantation in bone which comprises:

(a) a stem which has (i) a joint motion surface, e.g., a ball, at oneend, and (ii) an outside surface which extends away from the jointmotion surface and includes at least one tapered portion;

(b) a sleeve for fixation to the patient's bone which includes aninternal taper for locking engagement with the at least one taperedportion of the stem;

(c) a bone replacement element; and

(d) means for attaching the bone replacement element to the stem at alocation between the joint motion surface and the sleeve.

In certain embodiments of the invention, the means for attaching thebone replacement element to the stem comprises an internal locking taperwhich engages either a part of the same tapered portion of the stemwhich the sleeve engages or a separate tapered portion of the stem.

The bone replacement element can be composed of various materialsincluding bone, metal, plastic, and ceramic. When the material is bone,e.g., when the bone replacement element is a bone graft, the means forattaching preferably comprises a second sleeve which is affixed to thebone graft and has an internal taper for locking onto the stem. Also,when used with a bone graft, the stem preferably includes two taperedportions and a fluted portion between the tapered portions which engagesand cuts into the graft.

The sleeve(s) are preferably stepped and may be porous coated. Also, forbone replacement elements composed of metal, the outside surface of theelement may be porous coated to aid in the attachment of muscles,tendons, and other tissues.

To allow the surgeon to optimize the match between the prosthesis andthe patient's specific requirements, families of stems and sleeves, andfor certain embodiments, bone replacement elements, are provided to thesurgeon in the operating room. In this way, the surgeon can select thosecomponents which together provide the best overall fit and function forthe particular conditions presented by the patient.

The accompanying drawings, which are incorporated in and constitute partof the specification, illustrate the preferred embodiments of theinvention, and together with the description, serve to explain theprinciples of the invention. It is to be understood, of course, thatboth the drawings and the description are explanatory only and are notrestrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a prior art femoral prosthesis which includes astem and a bone replacement portion.

FIG. 2 is a side view of a prior art femoral prosthesis whose proximalportion has been configured to replace lost bone.

FIG. 3 is a side view, partially in cross-section, of a femoralprosthesis constructed in accordance with the invention for use with abone graft.

FIG. 4 is a side view, partially in cross-section, of a femoralprosthesis constructed in accordance with the invention having a stemwith two tapered portions, one for engagement with a bone replacementelement and the other for engagement with a sleeve which is implanted inthe patient's femur.

FIG. 5 is a side view, partially in cross-section, of a femoralprosthesis constructed in accordance with the invention having a bonereplacement element which is clamped to the prosthesis' stem and asleeve which engages a tapered portion of the stem.

FIG. 6 is a side view, partially in cross-section, of a femoralprosthesis constructed in accordance with the invention having a stemwith an elongated tapered portion for engagement with both a bonereplacement element and with a sleeve which is implanted in thepatient's femur.

FIG. 7 is an expanded view of the outside surface of sleeve 32 of FIGS.3-6 illustrating the use of steps or terraces on the outside surface.

FIG. 8 is a cross-sectional view along lines 8--8 in FIG. 5 illustratingrepresentative means for attaching a bone replacement element to theprosthesis' stem.

FIG. 9 is an expanded view of the outside surface of sleeve 34 of FIG. 3illustrating the use of steps or terraces on the outside surface.

FIG. 10 illustrates the use of a porous coating on the outside surfaceof sleeve 32 of FIGS. 3-6.

FIG. 11 illustrates the use of a porous coating on the outside surfaceof sleeve 34 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in FIG. 3 a femoral prosthesis 20 constructed inaccordance with the invention which incorporates bone graft 22.

Prosthesis 20 includes elongated stem 13 which has ball 24 at one endwhich serves as a joint motion surface. The outside surface of stem 13includes a first tapered portion 26 and a second tapered portion 28.Between the tapered portions are flutes 30. Stem 13 also includes asecond set of flutes 38.

Prosthesis 20 further includes first sleeve 32, second sleeve 34, andtrochanter washer 40 which is attached to stem 13 by screw 42. Firstsleeve 32 is implanted in the patient's femur 36 and provides strongmechanical fixation of the prosthesis to the proximal end of the femur.Additional fixation of the prosthesis to the femur is provided by flutes38 which help stabilize the distal end of the prosthesis with regard torotation about the prosthesis' longitudinal axis.

In practice, a series (family) of sleeves 32 of different sizes and/orconfigurations is provided to the surgeon so that he or she can choosethe sleeve which provides the best union with whatever portion of thefemur remains for implantation. Similarly, a family of stems 13 is alsoprovided to the surgeon so that again optimizing choices can be made atthe time of implantation.

As shown in FIG. 7, sleeve 32 preferably has a stepped outside surface48 of the type described in Noiles, U.S. Pat. No. 4,846,839, therelevant portions of which are incorporated herein by reference. As alsodescribed in that patent, if porous coating 58 is used, such coating ispreferably applied to just the sleeve and not to the stem (see FIG. 10).In this way, an opportunity for bone ingrowth is provided withoutputting the overall structural integrity of the prosthesis at risk.

As shown in FIG. 4, if desired, sleeve 32 can include a collar 44 forengagement with the exposed, proximal end of the femur. Similarly, asshown in FIG. 5, the sleeve can include a protruding portion 46constructed in accordance with Noiles, U.S. Pat. No. 4,790,852. It is tobe understood, of course, that the illustrated sleeves can be used withany of the prostheses of FIGS. 4-6. Whatever construction is used forthe sleeve's outside surface, its inner surface includes a taperedportion 50 for locking engagement with first tapered portion 26 of stem13.

The prosthesis of FIG. 3 includes second sleeve 34 for engagement withbone graft 22. Depending upon the size and shape of the bone graft,sleeve 34 can include various of the features discussed above withregard to sleeve 32. Thus, it can include a collar 44, a protrudingportion 46, a stepped outside surface 48, and, if desired, a porouscoating 58 or other coating to enhance adhesion when cement is used toaffix the graft. As with the first sleeve, whatever configuration ischosen for the outside surface of the second sleeve, its inner surfaceincludes a tapered portion 52 for locking engagement with second taperedportion 28 of stem 13.

In addition to sleeve 34, flutes 30 and trochanter washer 40 also helpaffix bone graft 22 to stem 13. The sleeve serves as the primary sourceof mechanical fixation between the graft and the stem. The flutesprovide further fixation by helping prevent rotation of the graft aboutthe stem as torque is applied to the graft by the patient's tendons andmuscles. Trochanter washer aids in the attachment of those tendons andmuscles to the prosthesis and also helps stabilize and strengthen thegreater trochanter portion of the graft. The combination of these threefixation mechanisms provides excellent stabilization of bone graftsincluding long bone grafts.

FIG. 4 shows an alternate embodiment 60 wherein a bone replacementelement 54 composed of metal is used in place of bone graft 22. For thisembodiment, as well as those shown in FIGS. 5 and 6, a series of bonereplacements is preferably provided to the surgeon so that a selectionof the most appropriate element can be made at the time of surgery.

As in FIG. 3, stem 13 includes a first tapered portion 26 which mateswith first sleeve 32. The stem also includes second tapered portion 28which mates and locks with taper 56 formed on the inside surface ofelement 54. As shown in FIG. 4, the outside surface of element 54 caninclude a porous coating 58 to aid in the integration and bonding of theprosthesis to the patient's tissues. Although not shown in FIG. 4,element 54 can also include a muscle/tendon attachment plate 62 of thetype shown in FIG. 5.

FIG. 6 shows a variation of the prosthesis of FIG. 4 wherein the stem'sfirst tapered portion 26 has been elongated so that it mates with theinternal tapers of both sleeve 32 and bone replacement element 54. Sucha construction can also be used with the bone graft embodiment of FIG. 3for applications in which flutes 30 are not required.

FIG. 5 shows a further variation of the invention employing a bonereplacement element 64 composed of plastic. Instead of locking tapers,this embodiment uses opposing flanges 66 and locking screws 68 to attachelement 64 to stem 13. Such an attachment system can also be used withthe metal bone replacement elements of FIGS. 4 and 6. Also, for aceramic bone replacement element, the attachment system of FIG. 5 can becombined with a taper lock of the type shown in FIGS. 4 and 6 to producea strong attachment.

The prostheses of the invention can be implanted using a variety oftechniques known in the art. Trial components are typically used toselect a set of components best suited to the patient's needs. Thepatient's femur is resected as necessary and a straight hole forreceiving stem 13 is reamed into the femur's medullary canal. A conicalcavity is then formed in the end of the femur for receiving sleeve 32.For sleeves including a protruding portion 46, a side cavity for thatportion can be formed in the end of the femur using a cutting tool ofthe type disclosed in U.S. Pat. No. 4,790,852, the relevant portions ofwhich are incorporated herein by reference.

The bone replacement element is affixed to stem 13 prior to itsimplantation. In the case of a metal element of the type shown in FIGS.4 and 6, fixation can be achieved by placing the element in anappropriate fixture and then applying a sharp impact force to stem 13 tolock the complimentary tapers on the element and the stem together. Fora plastic element of the type shown in FIG. 5, the element is slid overthe seem and then tightened into place using screws 68.

In the case of a bone graft, a cavity for the stem and sleeve 34 can beformed in the graft using techniques similar to those used to preparethe patient's femur. Sleeve 34 is then implanted in the graft, with orwithout cement, and the stem and sleeve are united by applying a sharpimpact force to the stem to lock together the complimentary tapers.

After the bone replacement element has been locked onto the stem, theprosthesis is inserted into the prepared femur by passing the stemthrough sleeve 32 into the straight cavity formed in the medullarycanal. As the stem moves into its final position, flutes 38 cut channelsinto the canal. As the last step in the implantation, the seem andsleeve 32 are locked together by applying a sharp impact force to thestem to engage tapered surface 26 with tapered surface 50.

The tapered surface(s) formed on stem 13 can have a variety ofinclinations. For example, taper angles of 6° total included angle forsurfaces 26 and 50 have been found to work successfully. Similar taperangles can be used for surfaces 28 and mating surfaces 52 and 56. Othertaper angles which can be used are in the range of from about 3° toabout 10°. For components made of a titanium alloy, preferred surfacesfor the interlocking tapers are a smooth machined surface on the stemand a recrystallized surface on the sleeve's internal taper as occursduring sintering of a porous coating.

The components of the prosthesis can be constructed from surgicallyimplantable materials such as chemically pure titanium or a titaniumalloy containing 6% aluminum and 4% vanadium for stem 13, bonereplacement element 54, and sleeves 32 and 34 (see ASTM SpecificationNo. F136) and ultra high molecular weight polyethylene for element 64.When porous coating is used, the coating can comprise small spheres orparticles of the same material as that used to form the underlyingcomponent.

Although specific embodiments of the invention have been described andillustrated, it is to be understood that modifications can be madewithout departing from the invention's spirit and scope. For example,although the invention has been illustrated in the context of a femoralprosthesis, it is also applicable to other artificial joints, such as,shoulder and knee joints. A variety of other modifications which do notdepart from the scope and spirit of the invention will be evident topersons of ordinary skill in the art from the disclosure herein. Thefollowing claims are intended to cover the specific embodiments setforth herein as well as such modifications, variations, and equivalents.

What is claimed is:
 1. A prosthesis for implantation in a bone which hasan end for receiving the prosthesis and a medullary canal, saidprosthesis comprising:(a) a stem comprising an elongated body having ajoint motion surface at one end and an outside surface extending awayfrom said joint motion surface, said outside surface including a taperedportion, said tapered portion being conically shaped with a circularcross section; (b) an elongated sleeve for fixation within an elongatedcavity created in the bone at the end of the bone for receiving thesleeve, said sleeve including an outer surface for engagement with saidcavity in the bone and an internal taper for locking engagement with thetapered portion, said internal taper being conically shaped with acircular cross section; (c) an elongated bone replacement element havinga longitudinal length; and (d) means for attaching the bone replacementelement to the stem at a location between the joint motion surface andthe sleeve, wherein (i) the elongated sleeve is spaced from the jointmotion surface by a distance which is greater than the longitudinallength of the bone replacement element and (ii) the stem extends beyondthe elongated sleeve by an amount sufficient for stabilizing engagementwith the bone's medullary canal.
 2. The prosthesis of claim 1 whereinthe bone replacement element is composed of a material selected from thegroup consisting of bone, metal, plastic, or ceramic.
 3. A prosthesisfor implantation in a bone which has an end for receiving theprosthesis, said prosthesis comprising:(a) a stem comprising anelongated body having a joint motion surface at one end and an outsidesurface extending away from said joint motion surface, said outsidesurface including a tapered portion, said tapered portion beingconically shaped with a circular cross section; (b) an elongated sleevefor fixation within an elongated cavity created in the bone at the endof the bone for receiving the sleeve, said sleeve including an outersurface for engagement with said cavity in the bone and an internaltaper for locking engagement with the tapered portion, said internaltaper being conically shaded with a circular cross section; (c) a bonereplacement element; and (d) means for attaching the bone replacementelement to the stem at a location between the joint motion surface andthe sleeve, said means comprising an internal taper for lockingengagement with the tapered portion, said internal taper being conicallyshaped with a circular cross section and being formed on an insidesurface of the bone replacement element.
 4. A prosthesis forimplantation in a bone which has an end for receiving the prosthesis,said prosthesis comprising:(a) a stem comprising an elongated bodyhaving a joint motion surface at one end and an outside surfaceextending away from said joint motion surface, said outside surfaceincluding a first tapered portion, said first tapered portion beingconically shaped with a circular cross section; (b) an elongated sleevefor fixation within an elongated cavity created in the bone at the endof the bone for receiving the sleeve, said sleeve including an outersurface for engagement with said cavity in the bone and an internaltaper for locking engagement with the first tapered portion, saidinternal taper being conically shaped with a circular cross section; (c)a bone replacement element; and (d) means for attaching the bonereplacement element to the stem at a location between the joint motionsurface and the sleeve, wherein the outside surface of the stem includesa second tapered portion, said second tapered portion being locatedbetween the joint motion surface and the first tapered portion, themeans for attaching comprises an internal taper for locking engagementwith said second tapered portion, and said second tapered portion andsaid internal taper are each conically shaped with a circular crosssection.
 5. A prosthesis for implantation in a bone which has an end forreceiving the prosthesis, said prosthesis comprising:(a) a stemcomprising an elongated body having a joint motion surface at one endand an outside surface extending away from said joint motion surface,said outside surface including a tapered portion, said tapered portionbeing conically shaped with a circular cross section; (b) an elongatedsleeve for fixation within an elongated cavity created in the bone atthe end of the bone for receiving the sleeve, said sleeve including anouter surface for engagement with said cavity in the bone and aninternal taper for locking engagement with the tapered portion, saidinternal taper being conically shaped with a circular cross section; (c)a bone replacement element; and (d) means for attaching the bonereplacement element to the stem at a location between the joint motionsurface and the sleeve, wherein the outside surface of the stem includesflutes for engagement with the bone replacement element.
 6. Theprosthesis of claim 5 wherein the bone replacement element is composedof bone.
 7. A prosthesis for implantation in a bone which has an end forreceiving the prosthesis, said prosthesis comprising:(a) a stemcomprising an elongated body having a joint motion surface at one endand an outside surface extending away from said joint motion surface,said outside surface including a first tapered portion, said firsttapered portion being conically shaped with a circular cross section;(b) an elongated sleeve for fixation within an elongated cavity createdin the bone at the end of the bone for receiving the sleeve, said sleeveincluding an outer surface for engagement with said cavity in the boneand an internal taper for locking engagement with the first taperedportion, said internal taper being conically shaped with a circularcross section; (c) a bone replacement element; and (d) means forattaching the bone replacement element to the stem at a location betweenthe joint motion surface and the sleeve, said means comprising a secondsleeve affixed to the bone replacement element and attached to the stem,said second sleeve being a separate element from both said bonereplacement element and said elongated sleeve.
 8. The prosthesis ofclaim 7 wherein said second sleeve includes an internal taper and saidsecond sleeve is attached to the stem through a locking engagement ofthe internal taper with the first tapered portion of the stem, saidinternal taper being conically shaped with a circular cross section. 9.The prosthesis of claim 7 wherein the outside surface of the stemincludes a second tapered portion located between the joint motionsurface and the first tapered portion, the second sleeve includes aninternal taper and is attached to the stem through a locking engagementof the internal taper with the second tapered portion, and said secondtapered portion and said internal taper are each conically shaped with acircular cross section.
 10. The prosthesis of claim 9 wherein theoutside surface of the stem includes flutes for engagement with the bonereplacement element, said flutes being located between the first taperedportion and the second tapered portion.
 11. The prosthesis of claim 7wherein at least a portion of the outer surface of the second sleeve isstepped.
 12. The prosthesis of claim 7 wherein at least a portion of theouter surface of the second sleeve is porous coated.
 13. The prosthesisof claim 7 wherein the bone replacement element comprises a preparedbone graft having a cavity formed therein.
 14. The prosthesis of claim 1wherein at least a portion of the outer surface of the bone replacementelement is porous coated.
 15. The prosthesis of claim 1 wherein at leasta portion of the outer surface of the elongated sleeve is porous coated.16. The prosthesis of claim 1 wherein at least a portion of the outersurface of the elongated sleeve is stepped.
 17. A prosthesis forimplantation in a bone, said prosthesis comprising two prostheticelements and a stem for attachment by locking tapers to the twoprosthetic elements, said stem comprising an elongated body having ajoint motion surface at one end and an outside surface extending awayfrom said joint motion surface, said outside surface including anelongated tapered portion which has a sufficient length to permitattachment of the two prosthetic elements and which is conically shapedwith a circular cross section for locking engagement with the twoprosthetic elements, each of the two prosthetic elements having aninternal taper which is conically shaped with a circular cross section.18. A prosthesis for implantation in a bone, said prosthesis comprisinga first prosthetic element, a second prosthetic element, and a stem forattachment by locking tapers to the first and second prostheticelements, said stem comprising an elongated body having a joint motionsurface at one end and an outside surface extending away from said jointmotion surface, said outside surface including first and secondelongated tapered portions each of which is conically shaped with acircular cross section, said first and second tapered portions beingseparated from one another along the length of the body, said firsttapered portion being for locking engagement with the first prostheticelement and said second tapered portion being for locking engagementwith the second prosthetic element, each of said two prosthetic elementshaving an internal taper which is conically shaped with a circular crosssection.
 19. The prosthesis of claim 18 wherein the outside surface ofthe stem includes flutes for engagement with one of the prostheticelements, said flutes being located between the first and second taperedportions.